JavaWeb监听器以及案例

╰+攻爆jí腚メ 2023-06-07 12:22 56阅读 0赞

# 对象监听器：request、Session、Application #

**监听内容：**创建、销毁、属性改变事件

**>实现ServletContextListener,HttpSessionListener,ServletRequestListener接口**

public class ContextSessionRequestListener implements ServletContextListener,HttpSessionListener,ServletRequestListener {
    
    	@Override
    	public void requestDestroyed(ServletRequestEvent arg0) {
    		// TODO Auto-generated method stub
    		System.out.println("监听ServletRequestEvent，销毁request对象");
    	}
    
    	@Override
    	public void requestInitialized(ServletRequestEvent arg0) {
    		// TODO Auto-generated method stub
    		System.out.println("监听ServletRequestEvent，创建request对象");
    		
    	}
    
    	@Override
    	public void sessionCreated(HttpSessionEvent arg0) {	
    		System.out.println("监听HttpSessionEvent，创建session对象");
    	}
    
    	@Override
    	public void sessionDestroyed(HttpSessionEvent arg0) {
    		System.out.println("监听HttpSessionEvent，销毁session对象");
    	}
    
    	@Override
    	public void contextDestroyed(ServletContextEvent arg0) {
    		// TODO Auto-generated method stub
    		System.out.println("监听ServletContextEvent，销毁context对象");
    	}
    
    	@Override
    	public void contextInitialized(ServletContextEvent arg0) {
    		// TODO Auto-generated method stub
    		System.out.println("监听ServletContextEvent，创建context对象");
    	}
    
    }

**>配置web.xml**

<listener>
      	<listener-class>org.threetierarc.listener.ContextSessionRequestListener</listener-class>
      </listener>

<listener-class>为路径全名。

# 对象属性监听器 #

**>实现ServletContextAttributeListener,HttpSessionAttributeListener,ServletRequestAttributeListener接口**

public class AttributeListener implements ServletContextAttributeListener,HttpSessionAttributeListener,ServletRequestAttributeListener {
    
    	@Override
    	public void attributeAdded(ServletRequestAttributeEvent arg0) {
    		// TODO Auto-generated method stub
    		String attrName=arg0.getName();//目前正在操作的属性名
    		Object attrValue=arg0.getServletRequest().getAttribute(attrName);
    		System.out.println("ServletRequest[增加]属性名"+attrName+"，属性值"+attrValue);
    	}
    
    	@Override
    	public void attributeRemoved(ServletRequestAttributeEvent arg0) {
    		System.out.println("ServletRequest[删除]属性名"+arg0.getName());
    		
    	}
    
    	@Override
    	public void attributeReplaced(ServletRequestAttributeEvent arg0) {
    //		例如：
    //		arg0.getServletRequest().setAttribute("name", "zs");
    //		arg0.getServletRequest().setAttribute("name", "ls");
    		String attrName=arg0.getName();
    		Object attrValue=arg0.getServletRequest().getAttribute(attrName);
    		System.out.println("ServletRequest[替换]属性名"+attrName+"，属性值"+attrValue);
    	}
    
    	@Override
    	public void attributeAdded(HttpSessionBindingEvent arg0) {
    		String attrName=arg0.getName();//目前正在操作的属性名
    		Object attrValue=arg0.getSession().getAttribute(attrName);
    		System.out.println("ServletSession[增加]属性名"+attrName+"，属性值"+attrValue);
    		
    	}
    
    	@Override
    	public void attributeRemoved(HttpSessionBindingEvent arg0) {
    		System.out.println("ServletSession[删除]属性名"+arg0.getName());
    		
    	}
    
    	@Override
    	public void attributeReplaced(HttpSessionBindingEvent arg0) {
    		String attrName=arg0.getName();
    		Object attrValue=arg0.getSession().getAttribute(attrName);
    		System.out.println("ServletSession[替换]属性名"+attrName+"，属性值"+attrValue);
    		
    	}
    
    	@Override
    	public void attributeAdded(ServletContextAttributeEvent arg0) {
    		String attrName=arg0.getName();//目前正在操作的属性名
    		Object attrValue=arg0.getServletContext().getAttribute(attrName);
    		System.out.println("ServletContext[增加]属性名"+attrName+"，属性值"+attrValue);
    		
    	}
    
    	@Override
    	public void attributeRemoved(ServletContextAttributeEvent arg0) {
    		System.out.println("ServletContext[删除]属性名"+arg0.getName());
    		
    	}
    
    	@Override
    	public void attributeReplaced(ServletContextAttributeEvent arg0) {
    		String attrName=arg0.getName();
    		Object attrValue=arg0.getServletContext().getAttribute(attrName);
    		System.out.println("ServletContext[替换]属性名"+attrName+"，属性值"+attrValue);
    		
    	}
    
    }

**>配置web.xml**

<listener>
      	<listener-class>org.threetierarc.listener.AttributeListener</listener-class>
      </listener>

**jsp测试代码：**

application.setAttribute("name", "zs");//增加属性
    	application.setAttribute("name", "ls");//替换
    	application.removeAttribute("name");//删除
    	
    	session.setAttribute("user","user1");//增加属性
    	session.setAttribute("user", "user2");//替换
    	session.removeAttribute("user");//删除
    	session.invalidate();
    	
    	request.setAttribute("sss","s1");//增加属性
    	request.setAttribute("sss", "s2");//替换
    	request.removeAttribute("sss");//删除

# 案例： #

1）统计当前在线人数（session）  
2）统计网页游览次数（application）  
注：自行配置web.xml  
**思路：**两个案例结合使用，在创建session时，在线人数首先拿application的数据+1，当退出或注销时(session失效时)，application则-1。

package org.userAction.listener;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    import javax.servlet.http.HttpSessionEvent;
    import javax.servlet.http.HttpSessionListener;
    
    public class userOnlineCount implements HttpSessionListener,ServletContextListener{
    
    	@Override
    	public void contextDestroyed(ServletContextEvent arg0) {
    		
    	}
    
    	@Override
    	public void contextInitialized(ServletContextEvent arg0) {
    		//获取application
    		ServletContext sc=arg0.getServletContext();
    		sc.setAttribute("count", 1);
    		
    	}
    
    	//session被创建时人数自增
    	@Override
    	public void sessionCreated(HttpSessionEvent arg0) {
    		ServletContext sc=arg0.getSession().getServletContext();
    		int count=(int) sc.getAttribute("count");
    		//存储
    		sc.setAttribute("count", ++count);
    		
    	}
    
    	@Override
    	public void sessionDestroyed(HttpSessionEvent arg0) {
    		ServletContext sc=arg0.getSession().getServletContext();
    		int count=(int) sc.getAttribute("count");
    		//存储
    		sc.setAttribute("count", --count);
    		
    	}
    
    }